Question 1100741
There are 9 choices for the book to place at the left end of the shelf.
Whatever book you choose,
there are 9-1=8 books to choose for the next place on the shelf.
So far, you had {{{9*8}}} different choices.
You keep choosing what book to place on the shelf to the right of the books already on the shelf.
Eventually, there are 5 books on the shelf and 9-5=4 books that were left.
The total number of different possible ways to place 5 of those 9 books on the shelf is
{{{9*8*7*6*5=highlight(15120)}}} .